Radio frequency distribution system



a March 16, 1937 HER S 2,073,933

RADIO FREQUENCY DISTRIBUTION SYSTEM Filed April 4, 1931 INVENTOR PHILIP J. HE ST ATrcSRNEY meme Ma -Q16, 1937 UNI-TED s'r ri-zs fPAraNT OFFICE.-

Radio Corporation of Delaware of America, a corporation Application April 4,1931, Serial No. 527,655

Claims. (01.178-45) My present invention relates to electrical distribution systems, and more particularly to a system for the collection and distribution of radio frequency signal energy.

6 Radio frequency energy distribution systems for apartment houses, hotels and the like are known, and have been described, for example, by J. Weinberger in his application Serial No. 350,869, filed March 29, 1929. In such systems 10 broadcast modulated radio frequency energy is collected by a single antenna, and distributed to a plurality of receivers located at isolated points in a building.

In the present application, there is disclosed an arrangementhaving as its main object the application of the principle of uniform loading to transmission lines for distributing collected broadcast energy to a plurality of independent radio receivers, the design of the lines being 0, such that a transmission line need not be broken at intervals for the insertion of loading coils.

Another important object of the present invention is to provide in an electrical system for distributing modulated radio frequency energy,

transmission cable of special construction, the

latter comprising a pair of insulated shieldedconductors, one of which conductors is spiralled about the other, the system requiring only a single amplifier between the antenna. and a plurality of receivers coupled to a transmission cable.

Other objects of the invention are to improve generally the simplicity and efliciency of electrical distribution systems, and more particularly to provide a radio frequency distribution system,

adapted for use in buildings and the like, which is not only reliable in operation, but economically produced and installed.

The novel features which I believe to be char- 40 acteristic of my invention are set forth in particularity in the appended claims, the invention itself however, as to both its organization and method of operation .will best be understood by reference to the following description taken in connection with the, drawing in which I have indicated diagrammatically one circuit arrangement whereby my invention may be carried into, effect.

In the drawing,

Fig. 1 shows a schematic outline of a system for distributing modulated radio frequency ene y.

' Fig. 2 shows in isometric a portion of a cable .1 used in the I system shown in Fig. 1, parts thereof being broken away.

Referring to the drawing wherein like characters of reference indicate the same elements in the different figures, Fig. 1 schematically shows a system for the distribution of radio frequency signals of broadcast frequencies to a large number of receivers l which are located at intervals along the transmission line 2. .As is well known, a single grounded antenna 3 is utilized for collecting broadcast energy.

The input of anaperiodic amplifier 4 is coupled to the common antenna. The amplifier is conventionally shown as. embodying at least one space discharge'tube, the resistor 4' representing the fact that the amplifier is aperiodic. The output of, the amplifier is connected to the transmission line 2, the latter comprising a pair of conductors 5, 5. The conductors are preferably disposed in a grounded shielding sheath 1, the conductor 6 (the high potential side of the transmission cable) being spiralled.

At intervals along the line 2, receivers l have their inputs connected to the conductors 5 and 6. Associated with eachcable are a plurality of coupling boxes 8, each box having disposed therein a coupling impedance 8, of proper value. While shown as resistors, the impedances 8 may be resistors, condensers, inductances, or suitable combinations thereof, and each impedance is usually connected, in line 6', between the high potential input terminal of a receiver and a point on conductor 6. The ground, or low potential, terminal of each receiver l is connected by a line 5' to an appropriate point on the grounded conductor 5, it being pointed out that each receiver is grounded by connecting the line 5, as at'9, to the coupling box 8 which is usually metallic and connected to the metallic sheath l of the transmission cable.

The coupling impedances 8' are necessary when devices, the impedance of which may become low, are coupled to the line 2 in order that it may not become'short circuited at such points.

A terminating resistor III is usually connected between the ends of conductors 5 and 6, at the end of a transmission line. In such a case, a box H (in contact with the metallic sheath 1) houses thev terminating resistor, the connected ends of the conductors being connected, as at -l l', to the box.

- Each receiver maybe of any conventional type, andusually embodies one, or more, tuned stages of radio amplification, a detector one, or more, stages of audio amplification, and a reproducer of "any type. Where the line 2 is of a short length, it is not essential to utilize themay be employed instead.

In Fig. 2 there is shown, in detail, the construction of the uniformly loaded radio frequency cable employed as the transmission line 2. In general, the cable comprises the pair of conductors 5, 6, the conductor 5 being disposed at the am's of the cable, and. being composed of either solid,

, wiring.

or stranded, wire. The conductor 6 is spiralled about the conductor 5 and is insulated therefrom. The layer 20 shows the usual insulation of the conductor 5. The layers 2i are braidings, wrappings, or other materials used to build out the diameter of the conductor 5, and, also, acting as insulation between conductors 5 and t. It is to be noted that the individual turns 22 of the spiral conductor 6 are insulated from each other by an insulation layer 23, the conductor 6 being either of solid, or stranded, wire. The two conductors 5 and 6 are covered with braiding 24 to form a cable which may be placed in conduit,

or armored.- I

Preferably, a shielding sheath 25 is employe for armoring the cable, and this sheath may be either ironconduit, armor-ing or metal braiding. In armoring, the cable, it is advantageous, but not necessary, to insulate the turns of the armoring from one another so that the effect of a shorted turn surrounding the cable will be eliminated. The cable is installed in the same manner as house wiring, and requires no special knowledge on the part of the man installing the Furthermore, the cable is enclosed; and of permanent construction, as-contrasted with systems which are installed on the outside of a building.

Some of the advantages of the present system of radio frequency distribution include the fact that the system requires only one amplifier between the antenna and a plurality of independent receivers coupled to a given transmission cable; the fact that receiver taps may be located at irregular intervals; the very important feature that the line need not be broken at intervals for the insertion of loading coils; the feature that the cable carries no high voltages; and the important advantage that since only one amplifier is employed, such disadvantages as tubereplacements, amplifier trouble and the like are minimized, and no extra house current wiring is necessary.

By feeding several amplifiers from the same antennaseveral transmission lines 2 may be run, thereby greatly increasing the number of receiver sets that can be operatedfrom a single antenna, as many as fifty receivers being adapted for connection to asingle transmission cable. It is also pointed out that there is no necessity for any switches other than those on the receivers themselves. Again, this type of low impedance radio frequency cable is of use in connection with television pick-up devices, and television studio wiring.

For example, this particularly is the case since satisfactory television service in an urbanarea is entirely dependent upon distribution throughout apartment houses. hotels and the like, of the television signal of intermediate frequency. Present distribution systems leave something to be desired for such television service, whereas by the present system it becomes feasible to dismy invention is by no means limited to the par- .ticular organization shown and described, but

that many modifications may be made without departing fromv the scope of my invention'as set forth in the appended claims.

What I claim is:

1. In combination with a plurality of space radio receiver sets and an aperiodic central antenna, a uniformly loaded aperiodic radio frequency transmission cable arranged to transmit radio frequency currents efficiently over a substantial distance consisting solely of two conductors connected one as a return for the other and consecutiveturns thereof being closely adjacent to provide a high and uniform radio frequency inductive reactance, one of said conductors being uniformly spiralled about the other, throughout the entire length thereof, the inner conductor beingconnected to the ground side of said antenna and sets, said spiralled conductor being connected to the high potential side of saidv antenna, a conductive connection including a high potential terminal of each of said receivers and said spiralled conductor, said conductors being completely insulated from each other, and said sets being connected to said conductors at irregular intervals along said cable.

2. A uniformly loaded, aperiodic, radio frequency transmission cable, adapted for interposition between an aperiodic central antenna and a plurality of spaced apart radio receiving sets, consisting solely of two conductors connected one as a return for the other, one of the conductors being adapted for efiecting a connection between the ground terminals of the sets and the ground side of the antenna, a plurality of layers of insulating braiding surrounding said last conductor,

the other conductor being provided with a thin insulation sheath and being wound inclosely ad- 'jacent spirals about the said layers for the entire length of said last conductor to provide a solenoid of appreciable radio frequency inductive reactance and said uniform loading, said layers of insulating braiding and said insulation sheath serving to separate said two conductors by a substantially large distance to provide a cable having sufficiently low capacity value to cause it to transmit radio frequency currents emciently over a substantial distance, said spiralled conductor being adapted to connect the high potential terminals of said sets to the high potential side of the antenna.

3. In combination with a plurality-of spaced apart radio receivers and an aperiodic antenna system, a transmission cable having one end coupled to said antenna and consisting solely of a central conductor covered by an insulation sheath, a plurality of layers of insulating braiding surrounding said conductorand forming a cylindrical insulating mass of large diameter, an outer conductor provided with an insulation sheath and wound in spiral formation about said insulating mass in close formation with adjacent turnsin contact, whereby the cable has a large inductance and small capacity per unit of length, a layer of insulation'material surrounding said outer conductor, a flexible metallic shield enclosing said insulation materialand cable, connec-. tions between the ground terminals of said receivers and said central conductor and a connection including a coupling impedance between the antenna terminal of each receiver and said outer conductor.

4. A flexible radio frequency aperiodic cable adapted for the ordinary methods of installing house-wiring, which includes a straight but flexible conductor, at least one flexible small solenoid of small good conductor wire having turns of small diameter concentric with said straight conductor, the number of turns being large per inch of length of the straight conductor slightly spaced apart, and such solenoid being flexible and extending continuously along the length of the cable; and flexible means insulating the straight and coiled conductors from one another; said combination constituting a balanced flexible radio frequency aperiodic cable of which the straight conductor is the balancing element of the combination, said cable being properly loaded with radio frequency inductive reactance distributed along the length of the cable by means of the radio frequency reactance of the long small solenoid itself.

5. A flexible radio frequency aperiodic cable adapted for the ordinary methods of installing house-wiring, which includes at least one small solenoid of small good conductor wire extending continuously along the length of the cable; a flexible insulating core around which said solenoid is wound in a large number of turns of small diameter per inch of length of the core and cable whereby the cable is loaded properly with radio frequency inductive reactance distributed along the length of the cable by means of the radio frequency inductive reactance of said long small solenoid itself; the turns of small wire being slightly spaced apart and such solenoid being flexible, and a flexible straight metallic wire extending inside said insulating core along the length of the radio frequency cable as a balancing element thereof.

PHILIP J. HERBST. 

